1. Field of the Invention
This invention relates to acrylate, hot melt, pressure-sensitive adhesives; more particularly to N-vinyl caprolactam-containing acrylate, hot melt, pressure-sensitive adhesives. More specifically, the invention relates to such adhesives which adhere well to human skin and are useful for medical products and which adhesives are polymerized compositions containing 2-ethylhexyl acrylate (2-EHA), isobutyl methacrylate (IBMA), N-vinyl caprolactam (NVCL) and optionally, but preferably, n-butyl acrylate (BA) as well, many of which adhesives adhere well to skin even under moist conditions.
The hot melt adhesive possesses the reversible properties of strong cohesive strength at ambient temperature and desirable melt viscosity at elevated coating temperatures. The present invention provides a process for making the hot melt adhesive as well as a process for making ostomy seals, adhesive tapes and bandages, wound drainage adhesive seals, wound dressings and the like that adhere to human skin and remain adherent even in a moist environment.
2. Prior Art
Although many adhesive compositions are known, very few of these are completely satisfactory for application to human skin. The requirements for such adhesives are stringent; they must adhere well to human skin during perspiration, when the weather is hot, or in an environment of draining wounds, yet be removable without leaving adhesive residue on the skin's surface. Numerous homopolymers, copolymers and terpolymers have been proposed for use as polymeric adhesives. The demands of modern technology, however, are for even higher requirements of adhesion and cohesion. Adhesion should take effect immediately on application to skin, even in a hot or moist environment, and should release cleanly when voluntarily removed in this environment.
Many acrylate homopolymers, copolymers and terpolymers previously used as medical adhesives lose adhesion in a moist environment. In the prior art, acrylic esters have been copolymerized with small portions of monomers such as acrylic acid, methacrylic acid, itaconic acid, acrylamide, methacrylamide, acrylic esters, vinyl esters, n-alkoxy-alkyl unsaturated carboxylic acid amides, half esters, half amides, amide esters, amides and imides of maleic anhydride, and the alkylaminoalkylene monoesters of maleic, itaconic or citraconic acids. Although the use of these compositions results in adhesives which adhere well to dry skin, many of these compositions lose adhesiveness in a hot or moist environment. U.S. Pat. No. 4,379,881 discloses an acrylic adhesive containing acrylic acid that adheres to skin under dry and moist conditions.
Not withstanding the utility and commercial success of acrylic pressure-sensitive adhesives, there are numerous applications of medical adhesives requiring such outstanding adhesive performance, in a moist environment, that presently available pressure-sensitive adhesives have not been entirely satisfactory. Thus, there is a need for pressure-sensitive adhesives having improved adhesion to skin for ostomy adhesive seals, wound drainage adhesive seals, surgical tapes, dressings, drapes, adhesive bandages, and the like.
In the past, attempts have been made to produce acrylicbased hot melt adhesives by incorporating 0.5 to 25% by weight of metallic chelating agents, such as zinc or cadmium salts to an amine-containing copolymer. The produced adhesives possess non-permanent, reversible bonds and showed an increase in Williams Plasticity Number from 0.93 to 1.25 mm (U.S. Pat. No. 3,925,282).
Another method found in the patent literature for improving cohesive strength of acrylic-based, hot melt adhesives is blending two copolymers, one copolymer containing a tertiary amine group, and the other has a built-in organic acid group. Upon mixing, a reversible ionic bonding is formed. (U.S. Pat. No. 4,405,517).
U.S. Pat. No. 4,337,325 (Shah), The Kendall Company, discloses hot melt, pressure-sensitive compositions comprising a blend of copolymers consisting of acrylic monomers and vinyl lactam, and can use N-vinyl caprolactam. The copolymer adhesive blend exhibits a viscosity less than 100,000 cps at 350.degree. F. (Applicant does not use blends, but rather uses only a single polymer component consisting of 3 or 4 monomers to make the adhesive of the present invention.)
U.S. Pat. No. 4,379,881 (R. F. Peck), Smith and Nephew Company, discloses an adhesive polyacrylate containing n-butyl acrylate, 2-ethylhexyl acrylate and acrylic acid that may be used for dressings and adheres firmly to skin under dry and moist conditions.
U.S. Pat. No. 4,164,614 (Ames), Eastman Kodak, discloses hot melt adhesive compositions containing 2-ethylhexyl acrylate, N-vinyl-2-pyrrolidone and styrene.
In addition, additional hot melt, pressure-sensitive adhesive compositions are disclosed in U.S. Pat. No. 4,423,182.
The prior art hot melt adhesives all differ significantly from those of the present invention in various respects particularly in lacking N-vinyl caprolactam (NVCL) which is a key component of the polymerized composition of the present invention. An improved hot melt, pressure-sensitive adhesive requires higher Williams Plasticity Numbers to avoid cold flow, above 1.5 mm. An adhesive for medical usage generally has higher requirements, such as no skin irritation, clarity, colorlessness, and higher moduli for lower adhesive transfer to skin. Hot melt adhesives from amine-containing monomers have a high tendency of discoloring and metallic chelating agents may cause skin irritation. Currently available hot melt pressure-sensitive adhesive exhibit acceptable tack, however, the cold flow, creep resistance and low modulus properties need improvement.
The novel hot melt, pressure-sensitive adhesives of the present invention utilize acrylic monomers which contain neither organic amine, nor acid functional groups, nor metallic salts. The hot melt adhesives of the present invention are polymerized compositions containing 2-ethylhexyl acrylate, isobutyl methacrylate, and N-vinyl caprolactam and may also contain, as an optional ingredient for the preferred adhesive, n-butyl acrylate.
It should be understood that while their medical uses will be emphasized herein, the adhesives of the present invention can also be used for various non-medical adhesive applications which may have much less stringent requirements in regard to various properties, and the less preferred adhesives of the present invention could be so used.
It is accordingly an object of the present invention to provide an improved medical pressure-sensitive adhesive. It is a further object of the present invention to provide a hot melt, pressure-sensitive adhesive having improved wear performance, particularly having good adhesion to skin under hot or moist conditions where skin perspiration or draining wound affects adhesion. The present invention further provides an economical process for making the adhesive composition and a method for coating the adhesive onto a substrate.